The use of photocurable dental materials in the practice of restorative dentistry has become popular. Photocurable materials are cured by exposure to radiant energy in a preselected spectral range in either the ultraviolet or visible spectrum. Presently, such materials are used as a replacement for silver amalgam to fill cavities anteriorly and posteriorly. Photocurable materials are also used to treat prosthetic appliances in the preparation of a dental restoration, such as a crown or bridge, and to repair broken teeth. Some of the advantages of using photocurable compositions include the ease of bonding the material to the tooth structure upon initiating the polymerization irradiation, the ease of color matching and the relatively low solubility of the material. One major disadvantage in the use of a photocurable dental material is shrinkage of the material during polymerization. Shrinkage from polymerization has been determined to progress in the direction of the source of light with the degree of shrinkage being proportional to the distance from the source of energy.
In a typical class II posterior restoration, the gingival floor represents a critical area for providing a good seal between tooth structure and filling material. The gingival floor is highly caries prone because it is located in between the teeth and sometimes subgingival. These conditions make it difficult for proper home cleansing to remove bacterial plaque. Thus, it is extremely important to achieve a good seal at the gingival floor of a restoration and to prevent microleakage which often results in tooth sensitivity and the development of a carious lesion.
In general, the dentist irradiates the photocurable material using a curing light which is directed to the site of the restoration through a light guide such as a fiber optic rod. The light guide is held in a direction so that maximum light energy strikes the occlusal surface, which corresponds to the direction that the restorative filling material is inserted.